Fatigue breakdown due to repeated stress depends on the number of times of the repeated stress and the stress amplitude (stress range) thereof. Accordingly, a method of examining an amplitude value of the repeated stress applied to material and the number of times (S-N curve) until breakdown and predicting a remaining life (fatigue damage degree and fatigue injury degree by literature) up to the fatigue breakdown using a minor law (cumulative fatigue damage law), is used.
In PTL 1, a frequency distribution of the stress amplitude with a level cross method from time series distortion data correlated with stress is calculated and a fatigue damage degree of vehicles is obtained by using the minor law.
In addition, as described in NPL 1, there is the rain flow method, as another method of obtaining the stress amplitude from time series stress data, and a method for extracting the stress amplitude from the time series stress data by using the method is described.